Add the cubed potatoes to your slow cooker. Add the chicken broth, milk, garlic powder, salt and pepper. Stir everything together. Cover with the lid and cook on high for 3½ to 4 hours. The potatoes should be fork tender when done.Add the butter to the potatoes and mash using a potato masher. Alternatively you can use a mixer to mix them until smooth, depends on what kind of consistency or texture you're going for.Stir in the sour cream and Parmesan cheese. Taste for salt and pepper and adjust as necessary.Garnish with chives and serve hot.